1. Technical Field
This invention relates to means for determining, specifying or prescribing adjustment or modification of the optics of the human eye by use of ophthalmic lenses or cornea shaping for the purpose of retarding, mitigating or controlling the progression of myopia. It also relates to ophthalmic correction devices, methods and associated therapies.
The adjustments or modifications concerned can be effected by the fitting of spectacle or contact lenses or, less preferably, by modification of corneal shape through ortho-keratology, corneal onlays or inlays, laser ablation and other forms of surgical intervention.
2. Discussion of Related Art
U.S. Pat. No. 7,025,460 to Smith et al and associated publications in the scientific literature show that the excessive eye growth associated with myopia—particularly in the young—is related to the focus of the peripheral retinal image and, more specifically, that myopia is encouraged where the focal plane of peripheral vision lies posterior of the retina and is discouraged or inhibited where it lies anterior to the retina. Lens designs based on this theory that provide both clear central vision and sufficient curvature of the peripheral focal plane were disclosed by Smith et al and are herein referred to as ‘anti-myopia’ lenses. Others have since disclosed various modifications and improvements of anti-myopia lenses for specific situations (see for example, Ho et al, US 20070159601).
Until the disclosures of Smith et al, it had been thought that myopia development had to do with some feature of central or paraxial vision and various methods of effecting selective defocus of the central image were proposed to inhibit myopia progression. As a result, central vision was impaired in one way or another in the attempt to inhibit myopia progression. For relevant prior patent disclosures see for example, Collins et al U.S. Pat. No. 6,045,578, Kris et al U.S. Pat. No. 6,343,861, Aller U.S. Pat. No. 6,752,499, Phillips US 2008062380, and, To US 2006/0082729. For relevant scientific publications see for example, Atchison, et al. “Shape of the Retinal Surface in Emmetropia and Myopia” (Invest Opthalmol Vis Sci. 2005: 46: 2698-2707); Mutti, et al. “Peripheral Refraction and Ocular Shape in Children” (Invest Opthalmol Vis Sci. 2000; 41:1022-1030); Saw, et al. “Interventions to Retard Myopia Progression in Children, An Evidence-based Update Opthalmology” (2002, Vol. 109, 3, 415-421); Schmid, “Variability of retinal steepness at the posterior pole in children 7-15 years of age” (Current Eye Research 2003, Vol. to 27, No. 1, pp. 61-68).
Traditionally, central vision correction for the myope (as opposed to the inhibition of progressive myopia) has been concerned with lower order aberrations that are readily measured using instruments commonly available to optometrists and are the major factors determining central visual acuity. The lower order aberrations concerned are essentially refractive error and astigmatism, which includes spherical and cylindrical components quantified in terms dioptric power and the orientation of cylindrical axis. These are specified or reflected in a typical ophthalmic prescription. Appropriate lenses can be obtained from such prescriptions using widely available computer-based design methods, or obtained from pre-manufactured lens stock. More detailed data, such as present cornea shape, will need to be provided were modification of cornea shape is desired.
More recently, techniques have been developed to further improve central visual acuity by correcting for higher order aberrations using wavefront techniques to prescribe and generate custom made contact lenses, spectacles, wave plates or corneal reshaping (see for example, Tuan US 2006/0264917, Andino US 2004/0246440, Rubinstein US 2003/0107706, Patel, U.S. Pat. No. 6,663,240 and Williams U.S. Pat. No. 5,777,719).
While the traditional methods that correct lower order aberrations provide good central vision for most myopes, they have the unfortunate side-effect of shifting the peripheral focal plane further behind the retina, rendering the patient more hyperopic in the periphery and giving added stimulus for eye elongation. And, while modern techniques that address both lower and higher order aberrations can provide excellent central vision, they can also have the same undesirable side effect in the periphery. On the other hand, the application of the teachings of Smith et al is not straight forward as it fails to adjust for important patient-related factors, allow for the problems of disturbing peripheral blur or recognise the role of conventional refractive correction in creating peripheral hyperopia.